Preliminary Studies On Attapulgite In Fertilizers

This paper is based on the prospect development that attapulgite is applied in thefertilizer, the modified attapulgite is developed to improve the adsorption capacity ofthe fertilizers ions. The attapulgite is modified with chemical methods and thermalactivation, and it is studied systematically to adsorpt the nutrient ions, which providesthe theoretical basis of the attapulgite’s efficient application in the fertilizer. The mainresults are:The attapulgite is modified by four typical quaternary ammonium cationicsurfactants, which are octadecyl trimethyl ammonium chloride, cetyl trimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride and sodiumdodecyl trimethyl ammonium chloride. The modified attapulgite is charactered by thegrafting rate. The best result is that attapulgite is modified by octadecyl trimethylammonium chloride. And the best conditions of modifying is: the dosage of octadecyltrimethyl ammonium chloride is35mmol/100g, the stirring time is15min, themodified temperature is70℃, the pH value is8, the highest grafting rate is98.89%.The study is done that the modified attapulgite by octadecyl trimethylammonium chloride adsorpts phosphorus, the adsorption process meets theFreundlich isotherm equation, and the dynamic adsorption process can better meet thequasi-two kinetic equation.The characteristic changes is studied that the calcined attapulgite adsorptsphosphorus at different temperatures, and it can be known that the calcinedattapulgite can adsorpt the maximum amount of phosphorus at500℃, and theattapulgite’s specific surface area is the maximum at this time.The adsorption characteristic is studied that the calcined attapulgite adsorptsphosphorus and nitrogen at500℃, and the adsorption process meets the Freundlichisotherm equation. The adsorption enthalpy change of N、P is positive. The adsorptionfree energy change is negative. The adsorption entropy change is positive. It is provedthat the adsorption process is endothermic and can be carried on spontaneously.The modified attapulgite by Octadecyl trimethyl ammonium chloride and being calcined at500℃is mixed with superphosphate. And when the total amount is100gand the amount of the attapulgite modified by Octadecyl trimethyl ammoniumchloride is10%of that, it can be seen from the experimental datas that the dissolutionrate of phosphorus is only32%at the seventh day. When the amount of the calcinedattapulgite at500℃is5%, and the dissolution rate is34.2%at the seventh day. Thedissolution rate is35.8%at the seventh day when the natural attapulgite is added in.